1. Technical Field
The present invention relates in general to the field of computers, and, in particular, to wireless devices. Still more particularly, the present invention relates to an improved method and system for reducing power consumption of a wireless device in a Local Area Network (LAN).
2. Description of the Related Art
Computer networks have greatly enhanced the computing power available to an individual computer by linking the individual computer to other computers and devices. Not only do networks provide for the exchange of information between autonomous computers, but they also enable each “node” in the network to share resources common to the entire network. Each node may be a computer, a data storage area, an output device such a printer or an interface to another network such as the Internet. Through resource sharing, application programs, databases and physical equipment in the network may be made available to any node without regard to the physical location of the node.
There are generally two types of network interconnections for connecting nodes. The nodes in a wired network communicate among themselves by using transmission lines, either electrical or optical, to carry signals between nodes. The nodes in a wireless network, on the other hand, communicate between nodes using radio frequency signals or other types of wireless communication media.
One type of wireless network is a wireless local area network (WLAN). WLAN's typically use high-frequency radio waves carrying digital data to communicate between nodes. Nodes in the WLAN communicate via transceivers at each node. Each transceiver both transmits and receives radio waves containing digital data. In a WLAN, nodes are typically defined as either base nodes or mobile nodes, in which the base nodes are stationary server computers providing an infrastructure/access point for mobile nodes, and mobile nodes are mobile computers, such as laptop computers, serving as a client device. Wireless communication can be between two stationary base nodes, between a base node and a mobile node, and/or between two mobile nodes. All nodes are within relatively close proximity to one another, such as within a building or an educational campus. The proximity of the nodes permits the network to operate reliably at low power and at high data rates.
Since a WLAN communicates wirelessly, the mobile nodes in the WLAN may be moved about to any location within a broadcast range of the WLAN. The mobile nodes typically are configured around one or more stationary base nodes, which coordinate the activity of the base and mobile nodes in the network. Alternatively, the network can be set up in a free configuration, where the mobile nodes communicate directly with each other without the use of base nodes to control network traffic.
Typically, mobile units wirelessly connected to the WLAN must continuously transmit and receive radio signals during time defined transmission cycles. Each transmission cycle correlates temporally to a multiple of a signal carrier's wavelength. Multiple units of datum may be transmitted during the transmission cycle by modulating either the amplitude or frequency of a carrier radio wave. While a small percentage of the transmission cycles are for communicating robust data from an application program or a website, most of the transmission cycles are used to maintain a communication link between the mobile node and the WLAN, typically between the mobile node and the base node, through the process of “pinging.” Pinging is a periodic transmission of an identifier signal between the mobile node and the base node that identifies the mobile node, and confirms to the base node that the mobile node is still wirelessly connected to the WLAN. Each identifier signal typically requires multiple transmission cycles.
To maintain the quality of data communicated across a WLAN, the number of units of data communicated within each transmission cycle is varied depending on the quality of a carrier wave signal. For example, in the Institute of Electrical and Electronics Engineers (IEEE) standard 802.11b for WLAN's, a constant number of symbols are transceived each second, where a symbol is the data transceived during one transmission cycle. The number of symbols transceived per second are either one million symbols per second (1 MSps) or 1.375 MSps, depending on the data transmission rate and how the data is modulated. For example, symbols transmitted at the rate of 1 MSps may be modulated using a technique called Binary Phase Shift Keying (BPSK) which results in one million bits per second (1 Mbps) of data being transceived. Symbols being transmitted at 1 MSps may alternatively be modulated using a more sophisticated modulation technique called Quadrature Phase Shift Keying (QPSK), resulting in 2 Mbps being transceived. Symbols transmitted at the rate of 1.375 MSps may be modulated using QPSK combined with Complementary Code Keying (CCK), which encodes 4 or 8 bits per symbol, resulting in the transceiving of 5.5 Mbps or 11 Mbps respectively.
In all scenarios defined by IEEE standard 802.11b, the nodes transmit and receive symbols at a rate of at least 1 MSps. This results in a high power demand on the nodes, which are continuously transceiving as described above.
Mobile nodes, such as laptop computer/transceiver units, are typically battery powered. While such units may run for several hours if only running a local stand-alone application, transceiving radio signals across the WLAN, such as prescribed by IEEE standard 802.11b, can double the power requirement of the unit, thus reducing the unit's effective battery life by 50%.
When the battery of the mobile node is effectively discharged, the laptop computer can no longer be used for computing or communicating with the WLAN, and important data and/or work may be lost. A spare battery can be carried with the laptop computer, but this adds additional inconvenience, cost and weight to the total unit. In addition, switching out batteries typically requires the laptop computer to be powered down, which is, at a minimum, an inconvenience, and has a potential consequence of causing the mobile node laptop computer to be off-line from the WLAN at a mission critical time. Furthermore, a large percentage of the cost and weight of such a mobile computer is taken up by the battery. Accordingly, to reduce battery weight and increase battery life, it is desirable to keep the mobile node's transceiver power usage and the accompanying battery drain at a minimum.
The constant transceiving of symbols at or above 1 MSps as described above results in the rapid draining of the mobile unit's battery. Thus, there is a need for a method and system that maximizes the battery life of a mobile node in a WLAN while keeping the mobile unit connected to the WLAN.